On August 8, 1805, Lewis wrote that Sacagawea “recognized the point of a high plain to our right which she informed us was not very distant from the summer retreat of her nation on a river beyond the mountains which runs to the west. this hill she says her nation calls the beaver’s head from a conceived remblance of it’s figure to the head of that animal. she assures us that we shall either find her people on this river or on the river immediately west of it’s source; which from it’s present size cannot be very distant. as it is now all important with us to meet with those people as soon as possible, I determined to proceed tomorrow with a small party to the source of the principal stream of this river and pass the mountains to the Columbia; and down that river untill I found the Indians; in short it is my resolusion to find them or some others, who have horses if it should cause me a trip of one month. for without horses we shall be obliged to leave a great part of our stores, of which, it appears to me that we have a stock already sufficiently small for the length of the voyage before us.”
Beaverhead Rock is within Beaverhead Rock State Park, located 14 miles south of Twin Bridges on Montana Highway 41. Although the rock is not publicly accessible, it is viewable from a parking area that includes interpretive wayside exhibits.